<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container {
            margin: 100px auto;
            width: 600px;
            height: 800px;
        }

        .header {
            width: 100%;
            height: 9%;
            background-color: #1b1b1b;
            text-align: center;
            line-height: 72px;
            color: white;
        }
        .center {
            height: 80%;
            width: 100%;
        }
        .center_top ,.center_bottom{
            display: flex;
            width: 100%;
            height: 49%;
            margin: 10px 0;
        }
        .c_t_left,.c_b_right {
            flex: 1;
            background-color: #1b1b1b;
            height: 100%;
            color: white;
            text-align: center;
            line-height: 320px;
        }
        .c_t_right,.c_b_left{
            width: 225px;
            background-color: #1b1b1b;
            height: 100%;
            color: white;
            text-align: center;
            line-height: 320px;
        }
        .c_t_left {
            margin-right: 10px;

        }
        .c_b_right {
            margin-left: 10px;
        }
        .footer {
            height: 9%;
            width: 100%;
            background-color: #1b1b1b;
            text-align: center;
            line-height: 72px;
            color: white;
            margin-top: 10px;
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="header">header</div>
        <div class="center">
            <div class="center_top">
                <div class="c_t_left">main</div>
                <div class="c_t_right">sidebar</div>
            </div>
            <div class="center_bottom">
                <div class="c_b_left">sidebar</div>
                <div class="c_b_right">main</div>
            </div>
        </div>
        <div class="footer">footer</div>
    </div>
</body>
</html>